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March 1962 Radio-Electronics
 [Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
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 Ever
the futurist, in 1962 Radio-Electronics magazine editor
Hugo Gernsback was making the case for
occupying millimeter- and submillimeter-wave bands. In fact, he first proposed
the concept back in 1959. He refers to it as "gap between the infrared (IR) and
radio regions." IR is generally understood to include wavelengths from around
750 nm (400 THz) to 1 mm (300 GHz). Gernsback cites work done by Professor Gwyn
O. Jones, of Queen Mary College of the University of London, with the claim that
among other advantages of millimeter-wave (mm-wave) is an ability to penetrate
certain wavelength "windows" in the atmosphere where lower frequencies do not
propagate efficiently, more "channels" of communications can be accommodated,
smaller antennas could be used, and narrower focused transmission beams possible
at mm-wave wavelengths would permit higher precision radar.
Unexplored Electron Gap
... Far-Reaching Discoveries Are Due in an Unknown Region ...
Possibly the most important unexplored region in the electromagnetic spectrum
lies in the band between the radio and the visible wavelengths. As we contemplate
the ultraviolet, then the visible, and next the infrared region, we come upon the
largely unknown "gap" of the extreme infrared or submillimeter waves which merge
into the radio millimeter waves.
The "gap" actually extends from 1/10-mm (one-tenth of a millimeter) to 1-millimeter
wavelengths. Microscopic as the gap is, it holds enormous possibilities for the
future. Scientists all over the world are working feverishly toward a breakthrough
in this unexplored region, which may well open up vast new domains in communication,
meteorological, astrophysical, thermonuclear research and space exploration - to
say nothing of its vital military importance.
While radio waves have been explored down into the millimeter regions,* no radio
or similar "contact" has ever been achieved across the submillimeter gap into the
extreme infrared territory.
The infrared band lies between the far end of the visible (circa 0.75 micron)
and the shortest microwaves (circa 1,000 microns). Since practically all bodies
(except those at absolute zero) radiate over this range, infrared detecting gear
is of great importance to the military. Nearly every target can be "seen" in the
dark because of the infrared energy it radiates; hence it need not be illuminated
by ordinary light, but can be detected with a "snooperscope" or similar device.
Infrared radiation is not "heat" in itself, and should not be confused with "heat
radiation."
There has been a great deal of speculation as to what we can expect when the
breakthrough of the gap between the infrared and radio regions is realized.
Professor Gwyn O. Jones, of Queen Mary College of the University of London, has given
some informative views on the subject in the December 14, 1961, issue of the New Scientist
(London):
"There are many signs of progress. So far, these have not been due to radical
advances in technique; no ultra-powerful source nor ultra-sensitive detector has
yet appeared. (At any moment both may appear, especially if the maser principle
is successfully applied at these wavelengths. It has already been used on both sides!)
Advance has come, rather, through the all-round improvement in electronic techniques
which has occurred since World War II.
"What is to be found at our extreme infrared or submillimetre wavelengths and
what uses will there be for techniques of handling such radiation? To answer the
strictly scientific question, one has only to observe how much of physical interest
is found on both sides [of the gap] and to realize the extent of the wavelength
gap to be filled in. There is enormous scope for studying the properties of matter
with radiation of these wavelengths. The properties studied will be, generally,
those concerned with large assemblies, such as those of atoms in crystals - just
as the classic and heroic early experiments of Czerny and Barnes in the far infrared
dealt with the main large-scale lattice vibrations of ionic crystals.
"A little unexpectedly, there is much of astrophysical and meteorological interest
at our wavelengths. Radiation from the Sun and Moon at about one millimetre wavelength
reaches the Earth in spite of the water vapour and carbon dioxide in the atmosphere,
which absorb heavily at shorter wavelengths. Such radiation from the Sun comes from
the outer part of the chromosphere, about which there is a great deal of speculation.
Observations on radiation from the Moon tells us about fluctuations in the temperature
of its surface and thence about its nature. There are suggestive differences between
the behavior of the infrared and centimetre-wave radiation arriving from the Moon
which point to the need for further observations in our region. There is the possibility
that atomic or molecular transitions occurring in outer space may give rise to detectable
radiation in our region. Much nearer home, it may be possible to turn to advantage
the heavy absorption by water vapour, and to study the formation of clouds and rain
by direct observations at appropriate wavelengths.
"There is no doubt that important technological applications would immediately
follow the development of powerful sources of extreme infrared, or submillimetre
radiation, particularly if the radiation had the coherent character of radio waves
(as does the radiation obtained from generators of the maser class) rather than
the incoherent character of the thermal radiation from hot sources. Radiation at
these wavelengths has at least three potential advantages for communication in radio
and radar. Because of the high frequency it would be possible to transmit a very
large number of independent signals without interference; narrow beams could be
transmitted with small aerials, and there is the possibility of transmission through
"windows" in the atmosphere (wavelength bands where absorption due to atmospheric
constituents is small). A Russian report of a window at about 0.35 millimetre wavelength
suggests that intensive work is proceeding in that country on the possibilities
of these wavelengths for communication.
"Finally, there is some possibility that coherent beams of submillimetre waves
might be used in the control of the very hot ionized gases or plasmas, in which
thermonuclear reactions might one day be sustained. As certain types of oscillations
of charged particles generate electromagnetic waves, so such waves will interact
with the particles themselves. It is a large step from the milliwatts or microwatts
of power now available at our wavelengths to the megawatts of power released in
thermonuclear reactions. Perhaps the really important applications of submillimetre
waves will turn out to be even more unexpected."
To the above we might add our own speculation. Since much of the electromagnetic
spectrum can be transformed into other forms of energy, for example light into electrical
energy, there can be other transformations between infrared and radio waves.
Let us mention only one. Imagine a parabolic reflector at whose focus we place
a submillimeter radio transmitter which can be adjusted to function also as an infrared
emitter or transmitter. We could then at will send out radio or infrared energy
- or both - and with a few additions, even coherent light. Using the same transmitter
as a receiver, we could then transform incoming light, or infrared radiation into
radiant radio or electric energy.
- Hugo Gernsback
* See also editorial "Millimeter Waves," in the June 1959 issue Radio-Electronics.
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